1. Field of the Invention
The present invention relates to apparatus and methods for testing printed circuit boards. More particularly, the present invention relates to apparatus and methods for checking all pins of through-hole components after installation to a printed circuit board to ensure that each pin protrudes therethrough sufficiently to allow soldering.
2. Description of Related Art
A wide variety of electronic devices employ printed circuit boards (PCBs). PCBs are boards for the mounting of components on which most connections are made by printed circuitry. Printed circuits (or soldered connections) are, in turn, printed wiring formed in a predetermined design in, or attached to, the surface or surfaces of a common base.
One example of a PCB is a computer motherboard. A computer motherboard is a generally rectangular component, made of plastic and strips of metal, designed to house a central processing unit (CPU) and related integrated circuits (ICs). Sockets are built into the surface of the motherboard, designed to hold the legs of the ICs. The legs, or pins, of the ICs are made of a stiff metal and they plug into IC sockets in much the same way electrical plugs slide into wall sockets.
Developments in the electronic arts have heretofore been driven in large part by a desire for components to do more while occupying less space. With respect to PCBs, this desire has caused more and more components, each with a large quantity of delicate pins, to be positioned on those boards in close proximity to each other. It is now not uncommon for a PCB to have over 1500 leads.
Notwithstanding the increased complexity caused by having more and more components attached closely together on a board, it has been and remains an important goal of PCB manufacturers to reduce, if not eliminate, defects.
Towards this goal, apparatus and methods for testing PCBs being manufactured have heretofore been developed.
One important requirement subject to testing is whether each pin of a through-hole component protrudes sufficiently through the PCB. It is important that all pins do so protrude so that good electrical contacts can be made during subsequent soldering processes. This test needs to be accurate because it is difficult to replace components once actually soldered, in whole or in part, to a board.
A prior art method of determining whether each pin of a through-hole component protrudes sufficiently through a PCB is visual inspection. During such an inspection, a board on an assembly line is picked up, turned over, and each through-hole visually checked to see if a pin is protruding through it.
The visual inspection method of testing PCBs has several defects. First, it requires considerable handling of the board, which can cause damage to delicate components. Second, the visual inspection method is time consuming. It can take quite a bit of time for a person to ensure 1,500 or more pins are protruding as required. Additionally, the visual inspection method is unreliable. Because many small delicate pins are often oriented in close proximity to each other, it is easy to miss the fact that one or more are missing or otherwise not protruding as they should.
A second method of checking all pins of through-hole components after installation to a PCB involves performance of an electrical continuity test. This test is directed to ensuring electrical continuity exists between the internal contacts of components above or on one side of the PCB and their corresponding pins below or on the other side of the PCB. Like the visual inspection test, the electrical continuity test has shortcomings and deficiencies. First, although this test can be performed in various ways, each involves physical contact with pins, which can damage them. Second, because the test does require that delicate contacts be made, which is inherently a time consuming process, performing this test increases PCB manufacturing time significantly. Third, it is not uncommon for internal contacts of components to be damaged during this test, which is wasteful and expensive.
Based upon the foregoing, those skilled in the art should understand and appreciate that it is a shortcoming and deficiency of the prior art that there has not yet been developed a quick, highly reliable, nonphysical-contact method for ensuring component pins protrude through a PCB enough to enable soldering.